Petroleum production technique

ABSTRACT

A method for the miscible displacement of petroleum from a subterranean reservoir is provided. The method involves injecting two miscible fluids into an injection well and producing petroleum from a production well. A first solvent, more dense than water, is injected into the reservoir near the top of the reservoir, and a second solvent, less dense than water, is injected into the reservoir near or at the bottom of the reservoir. Both solvents are followed by water. The first solvent will tend to flow downward and the second solvent will tend to rise. The solvents will blend and provide piston-like displacement through the reservoir.

unltea mates l'atent Allen et al. 1 Oct. 1, 1974 15 PETROLEUM PRODUCTIONTECHNIQUE 3.729.053 4/1973 Froning 166/273 [75] Inventors: Joseph C.Allen, Bellaire; Jack F.

Tate Houston Tex Primary Examiner-James A. Leppink [73] Assignee TexacoInc New York N Y Attorney, Agent, or Firm-T. H. Whaley; C. G. Ries [22]Filed: May 4, 1973 [57] ABSTRACT [21] Appl. No.: 357,405 A method forthe miscible displacement of petroleum from a subterranean reservoir isprovided. The 52 U S Cl ,2 l66/274 method involves injecting twomiscible fluids into an Ezlb 43/16 injection well and producingpetroleum from a prod 5 306 273 duction well. A first solvent, moredense than water, is l 1 0 earc 6/ injected into the reservoir near thetop of the reservoir, and a second solvent, less dense than water, is 56R f Ct d injected into the reservoir near or at the bottom of the l 1 eerences reservoir. Both solvents are followed by water. The

UNITED STATES PATENTS first solvent will tend to flow downward and thesec- 3,003,554 10/1961 Craig, Jr. et al. 166/274 ond solvent will tendto rise. The solvents will blend 3,047,063 7/1962 Connally, Jr. et al.166/273 and provide piston-like displacement through the res 3,221,81012/1965 Marx 166/269 ervoir 3,369,601 2/1968 Bond et al.. 166/2743,565,175 2/1971 Wilson 166/269 11 Claims, 3 Drawing Figures PETROLEUMPRODUCTION TECHNIQUE BACKGROUND OF THE INVENTION 1. Field of theInvention This invention relates to a process for recovering petroleumby miscible displacement.

2. Description of the Prior Art Various methods for inducing therecovery of petroleum from underground reservoirs are in existence.These methods include injecting water, .steam or some aqueous basedmixture to drive the oil from the reservoir. These displacementprocesses are inefficient. The inefficiency of these displacementprocesses is partly due to the retentive forces of capillarity andinterfacial tension. Miscible flooding provides a method for efficientlydisplacing the petroleum from a reservoir.

In miscible flooding, solvent for the petroleum is introduced into thereservoir and driven through the reservoir. Dissolution of the petroleumby the solvent permits no two phase system between the solvent and thepetroleum to exist at the conditions of temperature and pressureexisting in the reservoir. Therefore, the retentive forces ofcapillarity and interfacial tension are nonexistent. These forcesdecrease the displacement efficiency of a recovery process where thedriving fluid or displacing agent and the petroleum exist as two phasesin the reservoir.

In a miscible flood process the solvent has the capability of mixingcompletely with the petroleum in the reservoir. A transition zone isformed at the leading edge of the solvent between the solvent and thepetroleum in which miscibility exists between the solvent and thepetroleum. For economic reasons the solvent is normally injected as aslug followed by another fluid such as a gas or an aqueous fluid todrive the solvent slug and the petroleum through the reservoir.

In displacement processes in general, the ideal sought after ispiston-like displacement. That is, the displacing fluids should ideallypresent a flat front to the petroleum in the reservoir and displace ituniformly through the reservoir. Most miscible solvent slugs arefollowed by an aqueous fluid to drive them through the reservoir.Moreover, most miscible solvent injection methods have heretoforeinvolved only light hydrocarbons with densities less than water.Problems have arisen with such processes, however.

In a vertical miscible flood, for example, using a light hydrocarbonsolvent slug followed by water, the water will tend to finger throughtheless dense solvent, destroying piston-like displacement and resulting inpremature breakthrough of the displacing medium water. In horizontalmiscible flooding the light hydrocarbon solvents will tend to overridethe petroleum in the reservoir and leave much of it unrecovered,

SUMMARY OF THE INVENTION The invention is a throughput method for themiscible displacement of petroleum from a subterranean reservoirinvolving at least one injection point high in the reservoir and atleast one injection point low in the reservoir. A petroleum solvent moredense than water is injected into the injection point high in thereservoir followed by a driving fluid. A petroleum solvent less densethan water is injected into the injection point low in the reservoirfollowed by a driving fluid. The two solvent slugs are driven throughthe reservoir forcing petroleum to a production well where it isproduced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a hydrocarbon reservoirpenetrated by an injection well and a production well at the beginningof a flood.

FIG. 2 shows the same wells at an intermediate point of the flood.

FIG. 3 shows the same wells near the end of the flood.

DESCRIPTION OF THE PREFERRED EMBODIMENTS rations 14. Well 11 equippedwith conventional equipment which prevents fluid communication betweenfluids in the annulus l5 and the tubing 16. Well 12 has at least one setof perforations 17. A fluid 18 more dense and preferably of lowerviscosity than water is injected into the reservoir 10 through the upperperforations 13 via annulus 15 of well 11. A fluid 19 less dense andpreferably of lower viscosity than water is injected into reservoir 10through the lower perforations 14 via the tubing 16 of well 11. Thefluid 18 tends to flow downward in the reservoir while the fluid 19tends to rise in the reservoir. An aqueous fluid injected into bothupper and lower perforations following the solvents displaces thesolvent heavier than water 18 downward and the solvent lighter thanwater 19 upward as the fluids flow horizontally toward the producingwell 12. Aqueous fluid displacement of the solvents is very efficientdue to the favorable viscosity contrast, water viscosity being higherthan either solvent viscosity.

FIG. 2 shows the relative position of the solvent slugs after solventinjection has been terminated and an aqueous fluid has been injected fora short period of time. The aqueous fluid 20 is now forming a bankbehind the solvents and is drivingthe solvents in a vertical slugthrough the reservoir.

As the solvent slug migrates through the reservoir the two solventsbecome mixed with each other due to density differences. This isdepicted in FIG. 3.

A particularly preferred embodiment of our invention is to design thesolvent slugs so that a mixture of the solvents will have a densitysubstantially equal to water. Thus, with no density difference betweenthe solvent mixture and the displacing water, no segregation will occur,the slug retainsits identity and the petroleum displacement approaches apiston-like configuration. g

The above description is only typical, and many variations will beobvious to one skilled in the art after reference to the teachingscontained herein. For example, injection of the two solvents indifferent wells may provide substantially the same advantage ofinjection of both solvents in the same well. The character of thereservoir and location of the wells will enable one skilled in the artto choose a configuration that will most likely provide optimumperformance.

The solvents for use in our invention are of two general types, moredense than water and less dense than water. Those which are more densethan water should ideally also be substantially chemically inert towater and have solubility characteristics whichenable them to dissolveadequate amounts of petroleum. It is preferred that the more densesolvent have a viscosity less than water. Ideally, the solvent should becompletely miscible with the petroleum so that the interface between theleading edge of the solvent and the petroleum is removed. Examples ofspecific solvents include but are not limited to carbon disulfide andchlorinated hydrocarbons such as methylene dichloride and carbontetrachloride.

In certain applications carbon disulfide is the preferred heavier thanwater solvent because of its unique properties or ease of manufactureand recovery. In the case of tar sand oil, for example, the bitumen ismore soluble in carbon disulfide than in other solvents and certainbitumens may only be soluble to any appreciable extend in carbondisulfide. Also, where the recovered crude is to be catalyticallytreated in a refinery, for example, carbon disulfide is preferred. lt isa characteristic of covalently bonded halogens such as those found inhalogenated hydrocarbons that they tend to poison some refinerycatalysts. Carbon disulfide does not and in addition is quite easilyremoved from recovered crude by physical separation processes to bereused again, leaving the crude substantially free of carbon disulflde.Carbon disulflde may also have a great economic advantage overhalogenated hydrocarbons since it may be manufactured by the reactionbetween coke (carbon) and sulfur which are often found in excess nearpetroleum-producing areas.

It is also within the scope of our invention to use as the heavy solventa blend of carbon disulfide with another component, mutually soluble incarbon disulfide such as a chlorinated hydrocarbon. These materialsshould also be easily removed from recovered oil by physical separationtechniques such as vacuum distillation.

The solvent less dense than water to be used in our invention includesany aromatic or aliphatic hydrocarbon which will solubilize partially orcompletely the crude petroleum to be recovered. Examples of suitablesolvents include light crude oil and partially refined fractionsthereof, e.g., side cuts from fractionating columns, gas oils, kerosene,naphthas, straight-run gasoline, and liquifled petroleum gases. Purecomponents of any of the above are also suitable, for example, toluene,xylene, and benzene.

The size of solvent slug to be used will depend on the solvents chosenand the degree of recovery desired. The degree of recovery desired is amatter of economics and may be determined by those skilled in the artwithout engaging in inventive effort. As an aid in determining the sizeof slug needed the following procedure may be used but is not intendedto limit the scope of our invention or tie it to any routine calculationprocedure. The size of a slug of petroleum solvent, for example, may becalculated by a formula such as:

amount ofcrude per acre-foot of formation degree of depletion desired(decimal) Routine laboratory experimentation may be used to determinethe solubility of a given crude petroleum in the solvents used and coreanalysis will yield information on the amount of crude per acre foot offormation. Thus, the size of solvent slug for any field may bedetermined.

The driving fluid for use in our invention may be gaseous or liquid. Forexample, gases including light hydrocarbons and carbon dioxide may beused for the process of our invention. Aqueous fluids are particularlypreferred driving fluids in the process of our invention. Water, brineand thickened aqueous fluids are all suitable aqueous fluids for theprocess of our invention.

We claim:

1. A method for producingpetroleum from a subterranean reservoir whichcomprises:

injecting a slug of petroleum solvent more dense than water into theupper portion of the reservoir followed by a driving fluid,

injecting a slug of petroleum solvent less dense than water into thelower portion of the reservoir followed by a driving fluid and drivingthese solvents through the reservoir toward a production point wherepetroleum is produced.

2. A method as in claim 1 wherein the solvent more dense than watercomprises carbon disulfide.

3. A method as in claim 1 wherein the solvent more dense than watercomprises chlorinated hydrocarbons.

4. A method as in claim 1 wherein the solvent more dense than watercomprises mixtures of carbon disultide and chlorinated hydrocarbons.

5. A method for producing petroleum from a subterranean reservoir whichcomprises:

injecting a slug of petroleum solvent more dense than water into theupper portion of the reservoir followed by an aqueous driving fluid, I

injecting a slug of petroleum solvent less dense than water into thelower portion of the reservoir followed by an-aqueous fluid and forcingthese solvents through the reservoir with an aqueous driving fluidtoward a production point where petroleum is produced.

6. A method as in claim 5 wherein the solvent more dense than watercomprises carbon disulfide.

7. A method as in claim 5 wherein the solvent more dense than watercomprises chlorinated hydrocarbons.

8. A method as in claim 5 wherein the solvent more dense than watercomprises mixtures of carbon disulfide and chlorinated hydrocarbons.

9. A method as in claim 5 wherein the solvent slugs, if blended, wouldhave a density about equal to the aqueous driving fluid.

10. A method for producing petroleum from a subterranean reservoir whichcomprises:

simultaneously injecting a slug of petroleum solvent more dense thanwater into the upper portion of the reservoir and a slug of petroleumsolvent less dense than water into the lower portion of the reservoir,both solvent slugs followed by a driving fluid and driving these solventslugs through the reservoir toward a production point where petroleum isproduced.

11. A method as in claim 10 wherein the solvent more dense than water isselected from the group consisting of carbon disulflde and chlorinatedhydrocarbons and the driving fluids are aqueous fluids.

1. A METHOD FOR PRODUCING PETROLEUM FROM A SUBTERRANEAN RESERVOIR WHICHCOMPRISES: INJECTING A SLUG OF PETROLEUM SOLVENT MORE DENSE THAN WATERINTO THE UPPER PORTION OF THE RESERVOIR FOLLOWED BY A DRIVING FLUID,INJECTING A SLUG OF PETROLEUM SOLVENT LESS DENSE THAN WATER INTO THELOWER PORTION OF THE RESERVOIR FOLLOWED BY A DRIVING FLUID AND DRIVINGTHESE SOLVENTS THROUGH THE RESERVOIR TOWARD A PRODUCTION POINT WHEREPETROLEUM IS PRODUCED.
 2. A method as in claim 1 wherein the solventmore dense than water comprises carbon disulfide.
 3. A method as inclaim 1 wherein the solvent more dense than water comprises chlorinatedhydrocarbons.
 4. A method as in claim 1 wherein the solvent more densethan water comprises mixtures of carbon disulfide and chlorinatedhydrocarbons.
 5. A method for producing petroleum from a subterraneanreservoir which comprises: injecting a slug of petroleum solvent moredense than water into the upper portion of the reservoir followed by anaqueous driving fluid, injecting a slug of petroleum solvent less densethan water into the lower portion of the reservoir followed by anaqueous fluid and forcing these solvents through the reservoir with anaqueous driving fluid toward a production point where petroleum isproduced.
 6. A method as in claim 5 wherein the solvent more dense thanwater comprises carbon disulfide.
 7. A method as in claim 5 wherein thesolvent more dense than water comprises chlorinated hydrocarbons.
 8. Amethod as in claim 5 wherein the solvent more dense than water comprisesmixtures of carbon disulfide and chlorinated hydrocarbons.
 9. A methodas in claim 5 wherein the solvent slugs, if blended, would have adensity about equal to the aqueous driving fluid.
 10. A method forproducing petroleum from a subterranean reservoir which comprises:simultaneously injecting a slug of petroleum solvent more dense thanwater into the upper portion of the reservoir and a slug of petroleumsolvent less dense than water into the lower portion of the reservoir,both solvent slugs followed by a driving fluid and driving these solventslugs through the reservoir toward a production point where petroleum isproduced.
 11. A method as in claim 10 wherein the solvent more densethan water is selected from the group consisting of carbon disulfide andchlorinated hydrocarbons and the driving fluids are aqueous fluids.